Increasing tree cover threatens world’s most endangered antelope

Between 1985 and 2012, tree cover in hirola’s habitat has more than doubled.

This increasing encroachment by trees is likely to blame for the decline in hirola populations in Africa, researchers say.

Decline in elephant and cattle numbers in the region, an increase in browsing livestock, and increased drier conditions could have resulted in the increasing tree cover.

Expanding tree cover might sound like good news for wildlife. But for the hirola — the world’s most endangered antelope — trees may have spelled doom, according to a new study.

Once widespread across open grasslands along the Kenya-Somalia border, fewer than 500 hirola (Beatragus hunter) remain in the wild in Africa today.

Between 1985 and 2012, tree cover in hirola’s habitat increased by 251 percent, researchers report in the study published in the Journal of Applied Ecology. This increasing encroachment of the animal’s open grassland habitat by trees is likely to blame for their precipitous decline, they suggest.

“We were surprised by how quickly tree cover had increased in the geographic range of hirola,” Abdullahi H. Ali, lead author from the University of Wyoming, told Mongabay. “Tree cover had more than doubled over 25 years, at the expense of the grassland habitats on which hirola depend.”

Hirola herd in Tsavo East National Park. Photo by James Probert. From Wikimedia Commons, licensed under CC BY-SA 4.0.

Ali and his colleagues fitted nine adult female hirola with GPS collars and found that the animals avoided tree cover all-year-round.

They also found that increased tree cover across hirola’s historical geographic range was associated with several factors including decline in elephant and cattle numbers in the region, an increase in browsing livestock, and increased drier conditions.

Since elephants uproot and knock down trees, their loss from the region could have fueled growth of trees and a reduction in grasslands, the researchers suggest. Similarly, a shift in livestock — from grass-dependent cattle to browsing livestock — may have increased tree encroachment. Additionally, increasing drought and dried conditions might be favoring trees and reducing grasses in the hirola’s habitat, the researchers write. This could be because trees in the savannas have been shown to be better at withstanding water stress than grasses.

With much of hirola’s habitat encroached upon by trees, hirola populations are likely to remain low and will be susceptible to extinction, Ali said. “This underscores the urgency of bolstering population size of hirola in their last remaining habitats.”

This would require protecting hirola’s existing habitats, such as the Arawale National Reserve in eastern Kenya, the only formally protected area set aside for the conservation of the species. The researchers also advocate restoring the animal’s habitat across its historical range, calling it a “prerequisite to their recovery”.

According to Ali, restoration will need to include increased conservation of elephants (which help create grasslands), reseeding and fertilization of grasses, and more coordinated grazing of livestock by local pastoralists.

“Tree encroachment is reversible with support from both local communities and the conservation community,” Ali said. “We believe that each of the options [above] — alone or in combination — has strong potential to benefit hirola populations and human livelihoods simultaneously. We have implemented public outreach campaigns (employment of villagers as scouts, coordinated communication networks among villages) to raise awareness as to why hirola are so rare, and what can be done to improve the chances that they persist into the future.”

The hirola is the world’s most endangered antelope. Photo by James Probert. From Wikimedia Commons, licensed under CC BY-SA 4.0.

The little known hirola is the only surviving member of the once-widespread genus Beatragus. It is also classified as critically endangered by the International Union for Conservation of Nature (IUCN). Given its the phylogenetic distinctiveness as well as its rarity, the hirola has been listed as one of the ‘Top 100’ Evolutionarily Distinct and Globally Endangered (EDGE) mammal in dire need of enhanced conservation attention. The loss of the hirola would mean the first extinction of an entire mammalian genus on mainland Africa in modern human history.

“Today, the hirola is widely recognized as the most threatened antelope in the world. It is also Kenya’s most threatened ungulate,” co-author Rajan Amin of the Zoological Society of London, told Mongabay. “Ultimately, its conservation, which will also benefit many other threatened species including the African elephant and wild dog, will require long-term, community-based efforts that are compatible with human livelihoods.”